1. Field of the Invention
The present invention relates to a method of forming a deposited film, and more specifically to a method of forming a deposited film by reactive ionization, which is employed in the production of various semiconductor devices, and which comprises ionizing a reactive gas and thereby increasing the reactivity of it with particles of a raw material to deposit a film of a desired composition on a substrate.
2. Related Background Art
In already known reactive ion film forming methods, as represented by reactive sputtering and reactive evaporation, a reactive gas is supplied into a flying space of particles of a raw material, namely a space provided in a vacuum chamber and interposed between a source for generating particles of a raw material for a deposited film and a substrate, thereby causing a chemical reaction between the particles of the raw material and the reactive gas and forming a compound film on the substrate.
However, in case the chemical reaction between the raw material particles and the reactive gas is insufficient, the compound film obtained by the aforementioned known methods does not necessarily contain a component element of the reactive gas in a necessary amount, so that a desired film property often cannot be obtained.
In order to solve this problem and to sufficiently induce a chemical reaction between the raw material particles and the reactive gas, Japanese Patent Applications Laid-open Nos. 5-117847 and 6-151421 disclose a method of supplying a rare gas such as helium or neon together with a sputtering gas and a reactive gas into the flying space of the raw material particles.
The aforementioned patent applications disclose that with the supply of helium gas, helium atoms are excited in a plasma on the surface of a target, then the excitation energy of the helium atom is transferred to the reactive gas to ionize atoms of the reactive gas, and the ionized atoms of the reactive gas combine with the raw material particles by a high reactivity of the ionized atoms to form a compound film of a high quality.
However, the method disclosed in the aforementioned patent applications have a following problem. In case of a mere introduction of helium, neon or a mixture thereof into the flying space of the raw material particles, when argon constituting the sputtering gas has a high content in the rare gas, the electron temperature in the plasma on the target surface becomes equal to or less than an ionizing potential of argon (15.8 eV), whereby excited helium (about 19.8 eV or higher) or excited neon (about 16.6 eV or higher) having a higher excitation energy than that of argon ion cannot be sufficiently generated, so that the ionization of the reactive gas by the rare gas atoms in the excited state cannot take place in sufficient manner.
Also, when the content of argon is lowered to increase the content of helium, neon or a mixture thereof, the electron temperature is elevated close to the ionizing potential of helium or neon and also the number of excited species thereof increases to elevate the ionization rate of the reactive gas, but, in such case, the film formation rate is significantly lowered because of a decrease in the content of argon having a sputtering rate of 1 to 2 times of that of neon and 3 to 15 times of that of helium.
Consequently, a method of merely introducing helium, neon or a mixture thereof into the flying space of the raw material particles is unable to induce sufficient ionization of the reactive gas and is limited in the compatibility of improvement in the stoichiometry of the formed film and film formation rate.
An object of the present invention is to solve the problems in the aforementioned conventional technologies, and to provide a method of forming a deposited film by ionizing atoms of a reactive gas and particles of a raw material, increasing the reactivity of both at a surface of a substrate and reducing an aberration of a formed film from a stoichiometric composition, thereby forming a compound film of a high quality at a high film formation rate.
More specifically, a method of forming a deposited film on a substrate according to the present invention comprises:
a step of emitting particles of a raw material from a raw material particle generation source opposed to the substrate in a direction of the substrate;
a step of supplying atoms of a reactive gas in a flying space of the particles of the raw material, the space being interposed between the substrate and the raw material particle generation source;
a step of supplying atoms of a rare gas in an excited state to the flying space of the particles of the raw material to ionize the atoms of the reactive gas and the particles of the raw material; and
a step of forming a compound film on the substrate by a chemical reaction of the ionized atoms of the reactive gas and the ionized particles of the raw material.